The present invention relates to pacing leads for delivering electrical stimulation pulses to an organ, and more particularly to an improved pacing lead assembly having an electrode which is of a configuration to allow tissue from an organ to be stimulated to ingrow into the surface of the electrode to thereby anchor the electrode in a fixed position with respect to the organ.
Pacing leads generally comprise an electrode and a flexible insulative conductor for connecting an electrode to a pacer or a stimulator. In the case of cardiac pacing, the electrode is introduced through the vascular system into a cardiac cavity and is then moved into a position to contact the endocavitary wall of the heart. Various types of attaching devices are utilized to maintain the electrode in a fixed position with respect to the wall to be stimulated. For example, fins and tines are utilized to interlock in the trabeculi within the heart in order to prevent dislodgement of the electrode. Another type of pacing lead includes an electrode having a substrate which is coated with a plurality of small metal particles to form a network of interconnected pores over the surface of the electrode. Still another type of pacing lead includes an electrode in which a non-woven mesh material is placed over a mesh ball in order to form a porous tip.
Whenever a pacing lead is implanted, there is always the possibility that it will be desirable at some future date to withdraw or remove the lead from the organ to be stimulated. For example, it may become necessary to stimulate another part of the organ or it may be that the pacing lead has become damaged and must be replaced with a new lead.
In the case of the latter described pacing leads, which include an electrode formed of a mesh ball covered by a non-woven mesh screen, the surface formed of these materials serves to allow the ingrowth of soft tissue from the wall of the organ to be stimulated. When the tissue fibers have ingrown into the openings in the screen and mesh ball, the electrode is then retained in a fixed position with respect to the wall of the heart. One of the problems associated with this type of electrode construction is that the tissue fibers become so interwoven through the mesh screen and into the mesh ball, and it becomes very difficult to detach the electrode from the wall of an organ without causing localized damage to the organ. It is believed that the tissue fibers continue to grow and to become more interwoven throughout their entire length into the mesh ball thereby permanently bonding the fiber to the electrode. Accordingly, when one attempts to remove the pacing lead, it is necessary to literally tear the tissue fibers from the wall of the heart. Examples of prior implantable electrodes are disclosed in U.S. Pat. No. 4,156,429.